Radiant Exitance Research Articles

A two-step discrete method for reconstruction of temperature distribution in a three-dimensional participating medium

A new two-step discrete method is proposed in this paper for reconstruction of three-dimensional temperature distribution in an absorbing, emitting and isotropically scattering medium. With this new method, the temperature of the wall is also considered. The local radiative source term is reconstructed in the first step through the discrete transfer method from the directional, exit radiation intensities measured by CCD cameras. Then, the temperature of each discrete element is calculated in the second step by subtracting the scattering contribution from the retrieved radiative source term through the discrete ordinate method. The least squares minimum residual algorithm is employed to solve the ill-posed reconstruction equations and the calculation is improved to reduce the computational cost. The performance of the proposed method is examined by numerical test problems with unimodal and bimodal temperature distributions. The ill-conditioning of the reconstruction problem is checked by the Picard condition. The effects of the measurement noise and the radiative properties on the reconstruction accuracy are discussed. The results show that the method proposed in this paper is capable of reconstructing the temperature distribution accurately in large, confined, participating media, even with noisy input data. The computation time reduction of this new method is significant when compared with other methods.

Calibration and Uncertainty Analysis of an Optical Emission Spectrometer Measuring the Absolute Spectral Radiant Exitance of UV Signatures

AbstractAn optical emission spectrometer (OES) was designed and constructed to detect the absolute spectral radiant exitance of UV signatures for a wavelength range of 240 nm to 440 nm. Using a directly heated graphite black body furnace operating at a temperature of 3000 K, the spectral response of the OES in the UV range was calibrated. To evaluate the performance of the OES system, the emission spectra of molecules were measured in a butane flame and the absolute emissions of the UV signatures were calculated. The uncertainty of the absolute measurement of the UV signature was analyzed by considering various uncertainty budgets, and the total uncertainty of the OES was found to be 1.66 %.

High-power plasma radiator for pulsed and continuous irradiation

Based on a magnetically compressed discharge with an electromagnet, a high-power plasma radiator capable of operating in the pulsed, continuous, and combined regimes has been created. The radiant exitance of the discharge plasma reaches 2×105W∕cm2 in the pulsed regime and 104W∕cm2 in the continuous regime.

Automatic marker detection and 3D position reconstruction using cine EPID images for SBRT verification

In previous studies, an electronic portal imaging device (EPID) in cine mode was used for validating respiratory gating and stereotactic body radiation therapy (SBRT) by tracking implanted fiducials. The manual marker tracking methods that were used were time and labor intensive, limiting the utility of the validation. The authors have developed an automatic algorithm to quickly and accurately extract the markers in EPID images and reconstruct their 3D positions. Studies have been performed with gold fiducials placed in solid water and dynamic thorax phantoms. In addition, the authors have examined the cases of five patients being treated under an SBRT protocol for hepatic metastases. For each case, a sequence of images was created by collecting the exit radiation using the EPID. The markers were detected and recognized using an image processing algorithm based on the Laplacian of Gaussian function. To reduce false marker detection, a marker registration technique was applied using image intensity as well as the geometric spatial transformations between the reference marker positions produced from the projection of 3D CT images and the estimated marker positions. An average marker position in 3D was reconstructed by backprojecting, towards the source, the position of each marker on the 2D image plane. From the static phantom study, spatial accuracies of <1 mm were achieved in both 2D and 3D marker locations. From the dynamic phantom study, using only the Laplacian of the Gaussian algorithm, the marker detection success rate was 88.8%. However, adding a marker registration technique which utilizes prior CT information, the detection success rate was increased to 100%. From the SBRT patient study, intrafractional tumor motion (3.1-11.3 mm) in the SI direction was measured using the 2D images. The interfractional patient setup errors (0.1-12.7 mm) in the SI, AP, and LR directions were obtained from the average marker locations reconstructed in 3D and compared to the reference planning CT image. The authors have developed an automatic algorithm to extract marker locations from MV images and have evaluated its performance. The measured intrafractional tumor motion and the interfractional daily patient setup error can be used for off-line retrospective verification of SBRT.

Powerful wide-format quasi-steady-state radiator based on xenon tube lamps

This paper describes the design and technical characteristics of a wide-format radiator based on twenty special xenon tube lamps that makes it possible to irradiate objects up to 1m2 in area. The required amplitude-time characteristics of the radiant exitance of the radiator are formed by computer profiling the current pulses in each lamp. A thyristor line-supply system with electric power 3 MW is used in this case to generate one-second light pulses. Data are given on the structure of the radiator's light field and the results of physical modelling of pulses of complex shape with maximum irradiance 350W/cm2. The radiator is intended for studies of the action of powerful light on optoelectronic devices and optical and structural materials.

Inverse radiation problem of temperature distribution in one-dimensional isotropically scattering participating slab with variable refractive index

In this paper, an inverse analysis is performed for estimation of source term distribution from the measured exit radiation intensities at the boundary surfaces in a one-dimensional absorbing, emitting and isotropically scattering medium between two parallel plates with variable refractive index. The variation of refractive index is assumed to be linear. The radiative transfer equation is solved by the constant quadrature discrete ordinate method. The inverse problem is formulated as an optimization problem for minimizing an objective function which is expressed as the sum of square deviations between measured and estimated exit radiation intensities at boundary surfaces. The conjugate gradient method is used to solve the inverse problem through an iterative procedure. The effects of various variables on source estimation are investigated such as type of source function, errors in the measured data and system parameters, gradient of refractive index across the medium, optical thickness, single scattering albedo and boundary emissivities. The results show that in the case of noisy input data, variation of system parameters may affect the inverse solution, especially at high error values in the measured data. The error in measured data plays more important role than the error in radiative system parameters except the refractive index distribution; however the accuracy of source estimation is very sensitive toward error in refractive index distribution. Therefore, refractive index distribution and measured exit intensities should be measured accurately with a limited error bound, in order to have an accurate estimation of source term in a graded index medium.

SU-GG-T-38: Tracking of Brachytherapy Source Position Using Emission Imaging

Purpose: To construct an imagingsystem that uses the exit radiation from a brachytherapy source during treatment. This system uses a single flat panel detector(FPD) and is capable of tracking the source position in 3D space, with no extra imaging radiation source or extra radiation dose to the patient. Method and Materials: It uses one a‐Si FPD and BB tray. The BB plane is parallel to detector surface and has multiple BBs embedded with mechanical accuracy. When illuminated by an Ir‐192 HDR source, the BBs cast shadows on FPD. Based on the geometric relation between the BBs and FPD, coordinates of HDR source in 3D were derived: x s = x f 1 x b 2 /( x f 2 − x f 1 − x b 2 ), y s = y f 1 x b 2 /( x f 2 − x f 1 − x b 2 ), z s =− hx b 2 /( x f 2 − x f 1 − x b 2 ), y f 1 = y f 2 , where z is perpendicular to FPD, s denotes HDR source, f denotes FPD, 1 and 2 refer to two different BBs. A kVp source at 3.3 meters away was used to align the center BB with the center pixel on FPD. Image acquisition time was between 3 and 6 seconds per projection. For a HDR test plan of 11 dwell points, one projection was taken for each dwell point and the shadow of the BBs were manually identified from the projection images.Results: The 3D coordinates for the 11 dwell positions of the test HDR plan were all successfully reconstructed based on two BBs. As a simple consistency check, the relative distances between dwell points were compared with the expected values. The average of the difference is less than 0.05 cm with a standard deviation of 0.16 cm. Conclusion: With automated BB shadow recognition and faster FPD, this technique possesses the potential of tracking 3D trajectory of a brachytherapy source in real time, for real time position verification or dose reconstruction.

TU‐C‐351‐08: Application of Principal Component Analysis for Marker‐Less Lung Tumor Tracking with Beam's‐Eye‐View EPID Images

Purpose: Recent studies have shown the impact of beam's‐eye‐view (BEV) imaging during radiotherapy to monitor the tumor location. This information can be used for real‐time interventions, treatment setup and verification, adaptive radiotherapy and delivered dose calculation. Although the tumor‐lung tissue density contrast can be poor, we show that it can be sufficient for tracking without implanted markers. The pre‐treatment 4DCT information used to plan the treatment is employed to ascertain the tumor motion during the treatment. Method and Materials: Exit radiation is passively acquired during lung tumor radiotherapy by operating an EPID in cine mode. The cine‐EPID in‐treatment images and the pre‐treatment phase‐specific DRRs are registered and corrected for setup induced affine transformations. DRRs are made from each of the 10 phase bins from the 4DCT simulation scan. Principal Components Analysis is able to discriminate small differences between similar images by shifting the image space axes to cause significant differences. The multidimensional image space is generated using the collection of DRR and EPID images. Each image can be represented as a linear combination of the best principal components. Using the projection coefficients, a multidimensional distance between the images is computed to compare each in‐treatment image with the ten phase‐specific DRRs. The maximum similarity is found by computing the minimum distance between the images so the phase‐specific DRR and in‐treatment EPID image are matched. Results: We were able to attribute the phase information to at least 75 % of the acquired in‐treatment images. The methodology was tested on the DRR images alone with 90 % phase recovery. Conclusion: We have developed a PCA‐based algorithm that enabled us to quantify the differences between the tumor motion within the planning 4DCT and the actual tumor motion during the treatment. Conflict of Interest: This work was partially supported by Varian Medical Systems, Inc.

SU‐GG‐J‐66: Delivered Dose Assessment with Beam's‐Eye‐View Imaging During Radiotherapy

Purpose: During conventional radiotherapy the location of the patients' anatomy, particularly the tumor, while the treatment beam is on is of primary importance. This becomes especially relevant in treatment sites where large intra‐fraction motion has been observed (upper abdomen and thorax). We have already demonstrated a method for monitoring the target during irradiation with beam's‐eye‐view (BEV) imaging. In this work we use the intra‐fraction data to retrospectively calculate the delivered dose. This can be done in between each fraction and the cumulative treatment dose updated daily. If discrepancies are seen between planned and delivered, the treatment may be altered such that the delivered distribution converges with the plan. Method and Materials: The radiotherapy target is visualized daily during radiotherapy by collecting the exit radiation with an electronic portal‐imaging device (EPID). In between each fraction, the location of the target in the treatment images is compared with the reference position from simulation. The in‐treatment target positions are introduced in the treatment planning software as sub‐fields representing equal fractions of the original fields' monitor units. The dose distributions from each of the sub‐fields are summed to calculate the dose delivered each day. This distribution is updated daily to provide the cumulative delivered dose distribution. Results: The dose‐volume histograms (DVH) for the planned and delivered distributions have been calculated for several patients. Delivered doses to target and critical structures are generated for each fraction and cumulatively. Conclusion: The delivered dose can be calculated using the information contained in BEV images acquired during irradiation. By calculating the dose actually delivered to the target, we can assess our treatment procedures as well as more accurately report clinical results. Conflict of Interest: This work was partially supported by Varian Medical Systems, Inc.

Clinical Feasibility of Using an EPID in cine Mode for Image-Guided Verification of Stereotactic Body Radiotherapy

To introduce a novel method for monitoring tumor location during stereotactic body radiotherapy (SBRT) while the treatment beam is on by using a conventional electronic portal imaging device (EPID). In our clinic, selected patients were treated under a phase I institutional review board-approved SBRT protocol for limited hepatic metastases from solid tumors. Before treatment planning multiple gold fiducial markers were implanted on the periphery of the tumor. During treatment the EPID was used in cine mode to collect the exit radiation and produce a sequence of images for each field. An in-house program was developed for calculating the location of the fiducials and their relative distance to the planned locations. Three case studies illustrate the utility of the technique. Patient A exhibited a systematic shift of 4 mm during one of the treatment beams. Patient B showed an inferior drift of the target of approximately 1 cm from the time of setup to the end of the fraction. Patient C had a poor setup on the first day of treatment that was quantified and accounted for on subsequent treatment days. Target localization throughout each treatment beam can be quickly assessed with the presented technique. Treatment monitoring with an EPID in cine mode is shown to be a clinically feasible and useful tool.

SU-EE-A3-03: Automatic Target Position Verification with 3-D Reconstruction of Implanted Markers Using EPID Images

Introduction: In previous studies, a technique using an electronic portal imaging devices (EPIDs) in cine mode has been validated for tracking gold fiducials implanted in the liver for respiratory gating and stereotactic body radiation therapy. However, it was time-consuming and labor-intensive since the marker recognition was not performed automatically. In this study, we present an automatic algorithm to quickly and accurately extract the markers in EPID images and reconstruct their 3-D positions. Materials and Methods: The markers were placed in a solid water phantom. Images were acquired using a linear accelerator operating with the 6 MV photon beam at several gantry angles and couch angle positions. A sequence of images was created by collecting the exit radiation using the EPID in cine mode. The fiducials were recognized and detected using a sequence of filters including the Wiener, median, and Laplacian filters. The position of each seed in the EPID images was backprojected towards the source position at each beam angle. To reconstruct the optimized seed position in 3-D, the centroid and Gaussian fit were applied respectively to the distribution of the center points. Results: The average displacement between the seed positions reconstructed with the EPID images and the seed locations in 3-D CT image is measured to be 3.57 ± 2.59 mm (0.44–7.66 mm) using the centroid. Using Gaussian fit we can accurately reconstruct the marker locations with 0.98 ± 0.38 mm positioning error (0.39–1.47 mm) by significantly reducing the statistical error introduced by the outliers arising from anti-parallel beam projections. Conclusions: The 3D positions of implanted fiducials can be reconstructed using images from several beam angles. This algorithm will be used for patient data to find the average 3D target position during radiotherapy treatment. This work was partially supported by a grant from Varian Medical Systems, Inc.

Possibilities of dose reduction in lateral cephalometric radiographs and its effects on clinical diagnostics

The aim of the present study was to determine (1) the absorbed and the exit radiation doses for cephalometric exposures on a phantom head with various exposure settings and image receivers, and (2) the diagnostic image quality for various modalities assessed on cephalometric radiographs of patients. The dose measurements for lateral cephalometric radiographs were performed with a semiconductor detector, and also with thermoluminescent detectors and an Alderson phantom. Both the integral and the effective doses were determined. Two radiographs of each patient (n=119) were taken at two different times, one at a low tube potential setting, 75+/-5 kV, and one with a decreased dose. Film-screen systems with speed class 400 and one storage phosphor plate were used. Five observers assessed the radiographs for the visualization of six cephalometric reference points on a three-point scale with -1, 0 and 1. Twenty-seven image pairs were rescored to determine inter- and intrarater reliability. The statistical analysis was done using analysis of variance and Tukey's HSD (honestly significant difference) post hoc test. Increasing the tube potential setting led to an average dose reduction to 83% (integral dose) or to 87% (effective dose). Instead of taking the radiograph at a low tube potential setting (75 kV), a dose reduction of about 15% was feasible at a high tube potential setting (90 kV). A significant difference in reference point visibility existed between film radiographs at low tube potential settings (mean score 0.984) and at high tube potential settings (90 kV, mean score 0.958). For the storage phosphor plates, there was no significant difference to the film-screen combinations at low tube potential and halved milliampere seconds settings. In the second assessment, there was a high degree of agreement (96.6%) compared with the first assessment (unadjusted for random agreement). As there is only minimal dose reduction at increased tube potential settings, for a dose reduction, it seems to be more useful to use storage phosphor plates at unchanged tube potential and halved milliampere seconds settings compared with the film-screen combination.

Neutron dose in proton radiation therapy: In regard to Eric J. Hall (Int J Radiat Oncol Biol Phys 2006;65:1–7)

Dr. Hall ( 1 Hall E.J. Intensity-modulated radiation therapy, protons, and the risk of second cancers. Int J Radiat Oncol Biol Phys. 2006; 65: 1-7 Abstract Full Text Full Text PDF PubMed Scopus (869) Google Scholar ) comes to the conclusion that proton therapy offers an advantage with respect to scattered doses relative to photons only if pencil beam scanning (PBS) is applied but not for broad-beam modulated (BBM) beams. We disagree with this conclusion. 1Neutron dose depends on beam delivery parameters. Intensity-modulated radiation therapy, protons, and the risk of second cancersInternational Journal of Radiation Oncology, Biology, PhysicsVol. 65Issue 1PreviewIntensity-modulated radiation therapy (IMRT) allows dose to be concentrated in the tumor volume while sparing normal tissues. However, the downside to IMRT is the potential to increase the number of radiation-induced second cancers. The reasons for this potential are more monitor units and, therefore, a larger total-body dose because of leakage radiation and, because IMRT involves more fields, a bigger volume of normal tissue is exposed to lower radiation doses. Intensity-modulated radiation therapy may double the incidence of solid cancers in long-term survivors. Full-Text PDF Neutron dose in scattered and scanned proton beams: In regard to Eric J. Hall (Int J Radiat Oncol Biol Phys 2006;65:1–7)International Journal of Radiation Oncology, Biology, PhysicsVol. 66Issue 5PreviewDr. Hall’s Fig. 10 (1) is incorrect by a factor ≥9 to the detriment of scattered vs. scanned protons. We wish to clarify the source of neutrons in scattering systems, to correct his Fig. 10, and to put neutron doses into perspective. Full-Text PDF In reply to Drs. Macklis Gottschalk, Paganetti, et alInternational Journal of Radiation Oncology, Biology, PhysicsVol. 66Issue 5PreviewWe are indebted to Drs. Gottschalk, Paganetti, and colleagues for their elegant clarifications of the sources of whole-body neutron exposures in modern proton therapy facilities: their collective knowledge and experience in this field are unmatched. We should, at the outset, say that our comments relate to the optimal mode of delivery of radiotherapeutic proton beams—not to the potential advantages of protons versus photons. Full-Text PDF In regards to Hall: Intensity-modulated radiation therapy, protons, and the risk of second cancers (Int J Radiat Oncol Biol Phys 2006;65:1–7)International Journal of Radiation Oncology, Biology, PhysicsVol. 66Issue 5PreviewSeveral recent articles in the medical literature have discussed the risk of secondary cancers occurring within the treatment field, as well as at nearby or distant sites that have received appreciable doses from scattered or leakage radiation (1–5). Many new high-tech beam-shaping approaches such as intensity-modulated radiation therapy/image-guided radiation therapy produce more conformal dose deposition patterns, but also may result in large volumes of nontarget tissue receiving low but non-negligible doses of unintentional scatter and exit radiation outside the treatment field. Full-Text PDF

SU‐FF‐J‐08: A Novel Method for Image‐Guided Verification of SBRT with An EPID in Cine Mode

Purpose: The adoption of stereotactic radiosurgical techniques for extra‐cranial treatment sites is predicated on a high accuracy and precision of tumor localization before and during each treatment. We introduce a novel method for monitoring the tumor location while the treatment beam is on by using a conventional electronic portal‐imaging device (EPID). Method and Materials: In our clinic, we are currently treating some liver patients under a Phase‐I IRB‐approved extra‐cranial radiosurgery protocol. Prior to treatment planning, multiple (n &gt; 2) gold fiducial markers are implanted on the periphery of the tumor. At the time of treatment, the patient is placed in a stereotactic body frame with abdominal compression. After the set‐up orthogonal portal images are taken, the EPID is left in its acquisition position. When employed during treatment, the EPID, in cine mode, collects the exit radiation and produces a sequence of images for each field. By the end of treatment, a collection of images will be available in PortalVision for review. For advanced analysis and quantification, the images are exported and evaluated off‐line. Results: Given the length of hypofractionated treatments (due to the high dose delivered), we are able to acquire as many as 78 images for each field. The implanted gold markers are visible in the images even before processing. We use an in‐house program for calculating the location of the seeds and their relative distance to the planned location (as defined by the DRRs). Conclusion: We have developed an algorithm for quickly assessing target localization using implanted gold markers as surrogates. Not only is this information used to verify the treatment, but it may also be used in the future to adapt the treatment either for subsequent fields or remaining fractions. Conflict of Interest: This work was partially supported by a grant from Varian Medical Systems, Inc.

Metal/Fluorocarbon Pyrolants: VI. Combustion Behaviour and Radiation Properties of Magnesium/Poly(Carbon Monofluoride) Pyrolant

AbstractThe performance of poly(carbon monofluoride) (PMF) (synonym: graphite fluoride) (CFx)n, (1) as oxidizer in a fuel rich Mg based pyrolant (ξ(Mg)=0.45) is investigated. The radiance [W sr−1] under both static and dynamic conditions, the spectral radiant exitance [W cm−2 μm−1], the linear burn rate [mm s−1] and the mass consumption rate [g s−1 cm−2] have been determined. Calculations for enthalpy of anaerobic and aerobic combustion [kJ g−1] and for the equilibrium composition of the combustion products as well as combustion temperature are given. A mechanism for the reaction is discussed. The combustion product from Mg/(CFx)n surprisingly reveals the formation of single walled carbon nanotubes (SWCNT) and “carbon nano carpet rolls” (CNCR). For part V see Ref. [1].

Raman efficiencies of natural rocks and minerals: Performance of a remote Raman system for planetary exploration at a distance of 10 meters

Raman spectroscopy is a powerful technique for materials analysis, and we are developing and analyzing a remote Raman system for use on a planetary lander or rover. We have acquired data at a distance of 10 m from a variety of geologic materials using different instrument designs. We have employed a pulsed laser with both an ungated detector and a gated detector. A gated detector can reduce long-lived fluorescence while still collecting all Raman signal. In order to design a flight instrument, we need to quantify how natural surfaces will respond to laser stimulus. We define remote Raman efficiency of natural surfaces as the ratio of radiant exitance leaving a natural surface to the irradiance of the incident laser. The radiant exitance of a natural surface is the product of the sample radiance, the projected solid angle, and the full-width-half-maximum of the Raman signal. We have determined the remote Raman efficiency for a variety of rocks and minerals. The best efficiencies are achieved for large, clear, single crystals that produce the most radiant exitance, while darker fine-grained mineral mixtures produce lower efficiencies. By implementing a pulsed laser, gated detector system we have improved the signal detection and have generally decreased the integration time necessary to detect Raman signal from natural surfaces.

The instantaneous radiant exitance of non-static black holes

Selecting the advanced Eddington coordinates, and adopting the statistical method ,the instantaneous radiant exitance of non_static black hole is calculated. It is found that the instantaneous radiant emittance of non_static black hole is not only related to the radiant exitance by supposing it is in the state of thermal equilibrium, but also related to the rate of change and the temperature of its event horizon, and the absorption coefficient and the radiation coefficient of the black hole. In the situation of the spherically symmetric non_static black hole, the instantaneous radiant exitance of the black hole is always proportional to quartic power of temperature of the event horizon of black holes at anytime.

A one-dimensional inverse radiative transfer problem with time-varying boundary conditions

In this work are presented the formulation and solution of two inverse radiative transfer problems in one-dimensional homogeneous participating media with time-dependent boundary conditions. In the first one an energy balance for the incoming and exit radiation allows the direct determination of the absorption coefficient. In the second inverse problem we solve the simultaneous estimation of the total extinction and scattering coefficients using the source–detector method. We first consider a more general formulation of the direct radiative transfer problem, and then for the formulation of the inverse problems we use the particular cases of “cold medium” (no internal sources), transparent boundaries (no effects associated with differences on medium and environment refractive indices), and homogeneous media (constant radiative transfer properties). Test case results are presented.

Evaluation of Tungsten Cluster Radiation Dependent on Various Metal Halides

Tungsten cluster lamps are expected to yield high efficiency and excellent color rendering. However, a regenerative halogen cycle is required to form and maintain the small clusters within the microwave-excited high-pressure discharge. Metal halides play an important role in building the halogen cycle, but we still do not know how the metal halides affect the radiation characteristics of the tungsten clusters. We investigated the spectral radiant exitance, the luminous flux, and the color temperature of the tungsten cluster radiation in various metal halides, such as NaCl, KCl, CsCl, NaBr, KBr, CsBr, NaI and KI. The radiation from the tungsten clusters yielded a continuous spectrum with a maximum between 650 and 700 nm, although the spectra were dependent on the type of metal halide used. The luminous fluxes in the metal alkali bromides were twice as large as those in the metal alkali chlorides and iodides. Also, the luminous fluxes in the sodium halides were twice as large as those in the potassium halides, and four times as large as those in the cesium halides. From those results, we confirm that NaBr is suitable as a metal halide in tungsten cluster lamps.

Inverse radiative transfer problems in two-dimensional participating media

In the present work inverse radiative transfer problems in two-dimensional heterogeneous participating media are considered. An implicit formulation is used in which the cost functional of the squared residues between calculated and measured exit radiation intensities is minimized. The Levenberg–Marquardt method, a gradient-based minimization algorithm, is used, and therefore at every iteration of the iterative procedure the solution of the direct problem is required. For the solution of the direct problem, which is modeled by the linearized Boltzmann equation, the discrete-ordinates method with a finite difference approximation for the spatial derivatives is used. The inverse problems considered are related to the estimation of the absorption and anisotropic scattering coefficients, as well as the estimation of source terms.